Molecular deletion patterns in families from southern France with Duchenne/Becker muscular dystrophies

Molecular characterisation of Duchenne muscular dystrophy and phenotypic correlation

Dystrophin gene was analysed in 32 unrelated DMD families (46 subjects: 32 index cases and 14 sibs) for the presence of deletions by mPCR for 27 exons and cDNA probes for the entire gene. Deletions were identified in 32 patients (25 index cases and seven sibs) from 25 families. The concordance between the clinical phenotype and 'reading frame' hypothesis was observed in 24 (75%) cases. Of these, nine patients were wheelchair bound between 8-12 years of age, nine (age range 5-10 years) showed progressive difficulty in walking and six (age range 1.6-4 years) had onset of muscle weakness. One patient (CH), who was wheelchair bound at 12 years, the effect of mutation on the ORF could not be ascertained due to the presence of a junction fragment. Seven patients had inframe deletions of which four were wheelchair bound by the age of 13 years, and three (age range 5-7 years) although, ambulatory had difficulty in walking. There were eight patients who showed no deletion, of which four became wheelchair bound by the age of 12 years, four, though still ambulatory, were unable to run and tired easily. Correlation between phenotype and genotype of these DMD patients demonstrates that genetic studies of lymphocyte DNA may not always reflect the situation in the tissue involved in dystrophin, i.e. muscle. We describe a common dystrophin gene polymorphism in the Indian population with cDNA 11-14 that alters the Hind III restriction sites. Novel RFLPs were observed in 26 patients and their family members. Whether this is a polymorphism or, related to the diseased phenotype needs confirmation.

Mutation analysis in Duchenne and Becker muscular dystrophy patients from Bulgaria shows a peculiar distribution of breakpoints by intron

For the first time in Bulgaria, a deletion/duplication screening was performed on a group of 84 unrelated Duchenne/Becker muscular dystrophy patients, and the breakpoint distribution in the dystrophin gene was analyzed. Intragenic deletions were detected in 67.8% of patients, and intragenic duplications in 2.4%. A peculiar distribution of deletion breakpoints was found. Only 13.2% of the deletion breakpoints fell in the "classical" hot spot in intron 44, whereas the majority (> 54%) were located within the segment encompassing introns 45-51, which includes intron 50, the richest in breakpoints (16%) in the Bulgarian sample. Comparison with data from Greece and Turkey points at the probable existence of a deletion hot spot within intron 50, which might be a characteristic of populations of the Balkan region.

Molecular deletion patterns in Turkish Duchenne and Becker muscular dystrophy patients

The dystrophin gene deletion patterns of Duchenne/Becker dystrophy were investigated in 57 DMD, 7 BMD and 1 DMD-BMD intermediate muscular dystrophy patients. Deletions, analyzed by multiplex amplification of selected exons, were observed in 58% (38 cases) of the patients. It was found that exon 48 was the most frequently affected, while exon 44 was the least frequently affected. The number of deleted exons was variable, but single exon deletions were more frequent (41%) than larger deletions in our population and the great majority of deletions began distal to exon 44. The application of PCR to deletion analysis in D/BMD was found to be very useful in delineating the extent of the deletion in most of the cases (82%). It was seen that the frequency of deletion breakpoints in distal part of the dystrophin gene (exons 42-52) was detected in 64% of our cases. In our group, the frequency of deletion breakpoints in the same area of the dystrophin gene was between that of the French and the Finnish patients. The distribution of deletion breakpoints within the dystrophin gene of the Turkish population seems to have some differences from other populations. Deletion breakpoints were found to be clustered mainly in three separate regions covering introns 44, 45 and 50 within the central region of the dystrophin gene. Intron 44 was mostly 5' breakpoints but it was found not to be involved as 3' breakpoints. The correlation between phenotype and type of deletion agreed with the reading frame theory except for one DMD case.

Molecular analysis of the Duchenne muscular dystrophy gene in patients with Becker muscular dystrophy presenting with dilated cardiomyopathy

Molecular analysis of the Duchenne muscular dystrophy (DMD) gene was performed on 4 unrelated patients with Becker muscular dystrophy (BMD) presenting with dilated cardiomyopathy. Two patients with a deletion involving exon 1 were quite unique in that they developed fatal myocardial involvement in their teens, despite the absence of significant muscular weakness. The deletion found in these patients comprised the 3'-end of exon 1 and the greater part of intron 1. Two other patients with a deletion of exon 47 showed progressive muscular atrophy and weakness; they were considered to be typical BMD in both clinical features and the type of gene deletion. We speculate that a deletion around exon 1 may severely damage the expression and/or the function of dystrophin selectively in cardiac muscle, but not in skeletal muscle.

Diagnosis of dystrophinopathies: review for the clinician

The dystrophinopathies are muscle disorders due to an abnormality of an Xp21-linked gene which produces the dystrophin protein. The most common of these disorders are the Duchenne and Becker muscular dystrophies. Modern molecular genetic techniques enable reliable diagnosis and prognosis in many patients, but there are occasional pitfalls. Furthermore, the clinical spectrum of the dystrophinopathies are now such that the clinician needs to be aware of a broader range of clinical disorders that require analysis of the dystrophin gene and its product, not just those that mirror a classic Duchenne or Becker muscular dystrophy picture. This spectrum ranges from a severe form presenting at birth to asymptomatic elevation of CK. Females may be manifesting carriers or present as a severe phenotype when the abnormal gene is expressed as an X-autosome translocation or monosomy X. Laboratory diagnosis and prognosis can be made most accurately by using both DNA analysis at the dystrophin gene and immuno-analysis of muscle with antibodies directed against different regions of the protein product. This review describes some exemplary patients, suggests a clinical classification for dystrophinopathies, and outlines a diagnostic approach.